De-Novo Structural Elucidation of Acylglycerols by Collision-Induced Disso-ciation of Odd-Electron Ion Precursors and by Electron Activated Dissociation of Even-Electron Ion Precursors

State-of-the art mass-spectrometry can resolve double bond positions, fatty acid attachments and sn-positions of lipids but often lacks sensitivity, requires long reaction times and dedicated instrumentation. Atmospheric pressure photoionization using chlorobenzene as dopant (dAPPI) showed to form odd elec-tron (OE) ion precursors generating rich spectra by collision induced dissociation (CID). In this study 33 model acylglycerols were analyzed using dAPPI-CID for sn-position and double bond (DB) assignment. Acylglycerols with ≤ 3 DB formed OE ions [M-H]+ and those ≥ 4 DB M+. ions. OE-CID acylglycerol pre-cursors generated characteristic fragments intensity ratios for sn-positions and several DB fragment series. Compared to electron-activated dissociation (EAD) of even electron precursors formed by ESI, OE-CID showed better fragments intensities with shorter MS cycle times. For OE-CID de-novo DB assignments was performed by following loss series, such as M-CH3(CH2)n, with intensity maxima at the beginning of DB positions. For each DB lost, a Δ2H shift is observed (M-CH3(CH2)n Δ2Hx) and used for the annotation of following DB. Additional loss series were observed after fatty acid loss ((M-FA-3H-CH3(CH2)n), which showed sn-position related intensity alterations. This allowed to assign DB to specific fatty acids and eval-uate the stoichiometry of DB positions. MsRadaR, a R package with a de-novo structural elucidation pipe-line was developed for data visualization and to assign DB position, applicable for both EAD and OE-CID. Supercritical fluid chromatography coupled to dAPPI/CID was applied for the analysis of linseed oil where 36 acylglycerols were detected as radical cation. Furthermore, the approach was applied for the characteri-zation by SFC-APPI-CID of fatty acids and cholesteryl esters using SWATH analysis of standards and data dependent acquisition of plasma samples using selected monitoring mode as survey scan and en-hanced product ion as dependent scan.